A lot of things kept this game from being as good as it could have been.
Beautiful Graphics;
Exploring Rome is just great;
Ezio is still the main character;
Good ending;
Exploring tombs is back and still fun;
The Bad:
Weak story;
Full of "filler" missions;
Too short;
Characters from A.C II are back but are useless;
The help from the other assassin's is mostly useless;
Weak side-missions;
No use on building factions;
Finding Glyphs can be frustrating sometimes;
Some camera issues when climbing and jumping;
You don't get to explore outside of Rome;
Enemy A.I is a little too smart sometimes;
A.C Brotherhood is a beautiful looking game that feels hollow most of the time, and that can make you drop the game pretty fast. There are just too many useless, filler missions that should not be there at all.
The good thing is, the ending is very good, and it will keep you wondering "What happens next?".
Unfortunately, this game feels like a let-down and I would only recommend it because it's a straight follow-up to A.C II and you would be missing the story.